pgsql: Add items from Tom: < o Add a GUC variable to allow output of

Log Message:
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Add items from Tom:

< o Add a GUC variable to allow output of interval values in ISO8601
< format
212a211,223

o Add a GUC variable to allow output of interval values in ISO8601
format
o Improve timestamptz subtraction to be DST-aware

Currently, subtracting one date from another that crosses a
daylight savings time adjustment can return '1 day 1 hour', but
adding that back to the first date returns a time one hour in
the future. This is caused by the adjustment of '25 hours' to
'1 day 1 hour', and '1 day' is the same time the next day, even
if daylight savings adjustments are involved.

o Fix interval display to support values exceeding 2^31 hours
o Add overflow checking to timestamp and interval arithmetic

Modified Files:
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pgsql/doc:
TODO (r1.1693 -> r1.1694)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1693&amp;r2=1.1694)
pgsql/doc/src/FAQ:
TODO.html (r1.200 -> r1.201)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/TODO.html.diff?r1=1.200&amp;r2=1.201)